Method of making a dampening roller



' March 24, 1970 E. D. ILL 3,502,768

METHOD OF MAKING A'DAMPENING ROLLER Filed Nov. 25, 1966 mvmon 50/144 Q0Q ///ZL a%,m 00mm,

ATTORNEYS United States Patent 3,502,768 METHOD OF MAKING A DAMPENINGROLLER Edward D. Hill, 11212 Edgewater Drive, Cleveland, Ohio 44102Filed Nov. 25, 1966, Ser. No. 596,959 Int. Cl. B29c 1/04; B29h 9/10 U.S.Cl. 264-331 7 Claims ABSTRACT OF THE DISCLOSURE This invention relatesgenerally as indicated to a dampening roller for use in lithographicprocesses and to a method of making the same, and more particularly tosuch a roller having improved ability to effectively and efficientlytransfer dampening fluid.

In lithographic offset or planographic printing, a printing plate ischemically treated to provide printing and non-printing areas, with theprinting area, of course, being ink receptive and the non-printing areabeing water receptive. Pursuant to such treatment, a film of dampeningfluid is applied to the surface of the plate which is retained by thehydrophilic area but repelled by the ink receptive printing area,thereby separating and isolating the nonprinting area from the ink whichis applied to the printing areas. As a result, only the image of theprinting area is transferred to the blanket cylinder and onto the paperon which the image is printed.

To achieve successful printing by this method, it is necessary that thedampening fluid be applied to the surface of the printing plate inuniform and evenly distributed quantities and in regulated amounts toassure uniformly good quality reproduction of the printed image. In theapplication of such fluid, an arrangement of rollers is employed totransfer the dampening fluid onto the nonprinting areas of the plate.

Such arrangement of rollers commonly includes rollers known as dampeningrollers which are in contact with the printing cylinder and the platecarried thereon to apply and peripherally distribute a suitabledampening solution to the plate. Since dampening solutions are generallywater based solutions, the prior practice has been to use dampeningrollers which have a water absorptive surface such as a covering ofcotton, molleton, mole skin, etc. Due to the nature of such material,however, they tend to pick up and absorb particles of ink from the platewith which the dampening rollers are in contact and also to carry theink back into the dampening solution, thus dirtying the rollers andpreventing a clean layer of solution from being deposited on the plate.When this occurs, the. rollers must be cleaned and/ or replaced.

Various substitutes have been tried for the cotton or molleton rollersas for example a surface comprising a fabric of glass fibers coated withtetrafluoroethylene. It has been found, however, that with sustaineduse, the glass fibers are not satisfactorily maintained on the surfaceof the roller. Coverings of wool have also been tried, as well as rollersurfaces of glue-glycerin, but these also tend to pick up particles ofink and thus become inked up and dirty within relatively short periodsof time.

It is accordingly a principal object of the present invention to providea method of making such roller which is free from the above-mentioneddisadvantages of prior rollers.

3,502,768 Patented Mar. 24, 1970 Another object of this invention is toprovide a method of producing a dampening roller which has less tendencyto pick up ink than previously-known rollers and which will eifectivelyand efficiently transfer a film of dampening fluid.

Yet another object of this invention is the provision of a method ofproducing a dampening roller having a surface of a highly durablematerial which is capable of being readily cleaned by the use of lowgrade distillates or a solution of lye without having its surfaceadversely affected.

These and other objects are achieved by means of this invention in whicha dampening roller is provided having a water transfer surface of asmooth, substantially porefree normally ink-attractive plastic, such aspolyurethane or polyvinyl chloride. Such roller is produced by theprocess of this invention in which the interior of a roller mold isuniformly coated with a parting solution prior to molding of the roller.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawings:

FIG. 1 is a perspective view of the dampening roller of this invention;and

FIG. 2 is a cross-sectional view of such roller taken on the line 2-2 ofFIG. 1.

Referring now more particularly to the drawings, the dampening roller ofthis invention is designated generally by the numeral 1 and is seen ascomprising a central metal shaft 2 having a surrounding surface of asmooth, substantially pore-free plastic material 3. Contrary to thedampening rollers previously known, such plastic material is a normallyink-attractive material, such as polyurethane or polyvinyl chloride.

To produce the dampening roller of this invention, a roller mold iscoated with a substantially uniform coating of a parting agent. Theparting agent is not applied to the mold with a swab as in the usualprior procedure, however, as it has been found that it is not possibleto obtain a uniform coating from such method of application. Rather, theparting agent is applied to the interior of the mold in the form of asolution or suspension of the agent in a solvent.

Preferably, the roller mold is polished to a high degree prior tocoating with the parting agent, and is thereafter preferably preheatedto a temperature on the order of approximately -200 F. and filled with asolution of a parting agent, such as a wax, which has been dissolved ina suitable solvent such as, for example, trichloroethylene. The partingagent solution is generally heated to a temperature sufliciently high todissolve the agent, as for example approximately 180 F. in the case ofwax and trichloroethylene. A small opening is provided in the bottom ofthe mold, which permits the wax solution to be removed therefrom slowlyand evenly thereby applying a uniform coating to the interior of themold. The mold is thereafter charged with the desired plastic, and theroller is molded in the usual manner.

There are several parting agents which are suitable for use in thepresent invention, including various wax sub stances, such as Carnaubawax, spermacetti wax, Chinese wax or beeswax. Similarly, suitableparting agents include silicone based substances such as siliconegreases.

The parting agent is dissolved in a suitable solvent, which may be anysolvent capable of dissolving the particular agent in question.Preferably, the solvent will be highly volatile, low boiling solvent,such as the various halogenated hydrocarbons, including chlorinatedhydrocarbons such as trichloroethylene, tetrachloroethylene,chloroprene, chlorobenzene, etc. and aromatic hydrocarbons such asbenzene, toluene, xylene and naptha. As mentioned, the solvent ispreferably highly volatile, as this will facilitate drying and hence theapplication of a uniform coating to the interior of the mold.

The amount of parting agent in the solution may be varied, but isnormally Within the range of approximately 1 to about 10 weight percent,and preferably within the the range of about 2 to about by weight. Ithas been found that better results are produced if the quantity ofparting agent is kept Within the specified general limits, as the use oftoo much of such agent produces a coating which is of such thicknessthat it Will not readily dry on the surface of the mold.

As mentioned previously, the plastic material comprising the surface ofthe dampening roller is an ink-attractive material rather than thehydrophilic or water absorptive materials previously used. An example ofsuch material is polyurethane, particularly polyester-basedpolyurethanes, as for example, those produced by reacting a branchedadipate polyester with a diisocyanate.

A particularly suitable polyurethane is that disclosed in my co-pendingapplication Ser. No. 483,263 filed Aug. 27, 1965 and entitled Roller forApplying Paint, Ink and the Like. In general, such polyurethane isformed by reacting a polyethylene glycol, a polyol and an isocyanate.

Materials other than polyurethanes may also be used for the surface ofthe dampening roller, as for example polyvinyl chlorides. An example ofa suitable such polyvinyl chloride is that disclosed in US. Patent2,631,358. which may be formed by reacting a polyvinyl chloride resinwith a high boiling plasticizer such as dioctyl phthalate. A suitablepolyvinyl chloride composition comprising approximately 4 parts ofplasticizing agent to one part of pvc resin and including the usualinhibitors such as tribasic lead sulfate, ricinoleate of tin, etc. Willproduce a satisfactory roller surface.

The dampening rollers of this invention have been found to perform quitesatisfactorily in the transfer of dampening fluids in offset printingoperations. The plastic surface of such rollers has a highly polished orglassy appearance and is exceptionally smooth and pore-free. As a resultof this, the roller is able to provide an actual sheet or film ofdampening fluid which is very effective in separating the ink-attractiveroller surface from the ink contained on the printing plate. Thisability to transfer a sheet or film of fluid is in contrast topreviously known dampening rollers which have tended to produce apattern of dots of fluid due to the hydrophilic or water absorptivenature of the surface. As can be readily appreciated, such surfaces areless capable of preventing contact with the ink on the printing platethan the roller of the present invention which transfers an actual filmof fluid.

This invention will be better understood by reference to the followingspecific but non-limiting example.

Example Approximately 5% of Carnauba Wax was dissolved intrichloroethylene by heating to approximately 180 F. Such solution wasthereafter poured into a highly polished roller mold, which waspreheated to approximately 180-200" F., until such mold was completelyfilled. Thereafter, the wax solution was permitted to slowly and evenlyrun out from the bottom of the mold, and thus an even and uniformcoating was applied to the interior of the mold.

A metal roller shaft was thereafter centered within the mold and themold was charged with the following polyurethane composition:approximately parts by weight of polyethylene glycol having a hydroxylnumber of 55 (heated to approximately F. to place it in liquid form),7.5 parts by weight of trimethylolpropane and 12.7 parts of MondurI'D-80 toluene diisocyanate. The mold was thereafter heated toapproximately 250 F. and permitted to remain there for approximately 2hours to cure.

Such roller was subsequently used in a lithographic offset printingpress and was found to perform quite satisfactorily in the transfer ofdampening fluid to the printing plate without being adversely affectedby the ink present on the printing plate.

It will thus be appreciated that the dampening rollers of this inventionhaving a smooth, pore-free or glassy surface of an ink attractiveplastic have distinct advantages over the cotton or molleton coveredrollers previously known. Additionally, such rollers have been found toremain substantially free of ink deposits for extended periods of timeduring operation on a press. Similarly, because of the durable nature ofthe surface of such rollers, they may very readily be cleaned if any inkis picked up, simply by cleaning with a low grade distillate or asolution of lye and water.

I therefore particularly point out and distinctly claim as my invention:

1. A process of making a dampening roller comprising substantiallycompletely filling the interior of a roller mold with a solution of aparting agent in a suitable solvent comprising approximately 1 to about10 Weight percent of such parting agent, slowly and evenly removing suchsolution from such mold thereby applying a substantially uniform coatingto the interior surface thereof, charging such coated mold with anormally ink attractive plastic composition, and applying sufiicientheat to such mold and composition to form a dampening roller having asmooth, substantially pore-free surface effective to transfer a film ofdampening fluid.

2. The process of claim 1 in which such parting agent is a wax.

3. The process of claim 2 in which such solution comprises approximately2 to about 5 weight percent of such wax.

4. The process of claim 3 in which the solvent for such solution istrichloroethylene.

5. The process of claim 1 in which such mold is heated prior to fillingwith such solution.

6. The process of claim 1 in which such plastic is a polyurethane.

7. The process of claim 1 in which such plastic is polyvinyl chloride.

References Cited UNITED STATES PATENTS 2,491,097 12/1949 Feagin l855.13,101,244 8/1963 Hood 264-338 2,908,040 10/ 1959 Schneider 1l7-942,045,913 6/1936 Hoy 106-3825 3,002,866 10/1961 Gartrell 2643382,536,323 1/1951 Spencer 1l794 ROBERT F. WHITE, Primary Examiner R.SHEAR, Assistant Examiner U..S. Cl. X.R. 264338

